1. Field of the Invention
The present invention relates generally to telescopes and, more particularly, to telescope tubes and to altitude-azimuth telescope mounts for supporting telescope tubes.
2. Brief Description of the Related Art
Telescopes generally comprise a telescope tube containing various optics for magnification and a telescope mount for supporting and positioning the telescope tube. Telescope tubes typically have an imaging end that is pointed at an object in the sky and a viewing end carrying an eye piece by which a magnified image of the object is viewed. The telescope tubes may have end rings at the imaging and viewing ends, with the end rings having an external diameter larger than the cylindrical bodies of the telescope tubes. Various materials have been proposed for the cylindrical bodies of telescope tubes including metal, plastic and cardboard. The materials conventionally used for the cylindrical bodies of telescope tubes present numerous disadvantages including difficulties associated with manufacturing, lack of durability, relatively low strength to weight ratio, lack of sufficient stiffness to hold the optics in their proper position, the inability to absorb vibrations that result in a degraded image, inadequate moisture resistance, the need for specialized coatings which add excessive weight and manufacturing complexity, relatively high specific heat resulting in an undesirable storage of thermal energy, invasion of the optical path by convection currents transferring dissipated heat with resulting degradation of image sharpness and stability, and lack of aesthetic appeal.
Wood offers several advantages over other materials more commonly used for the cylindrical bodies of telescope tubes. Wood is easier to shape, modify and repair, and is of greater durability than many materials conventionally used for the cylindrical bodies of telescope tubes. Wood has a higher strength to weight ratio than materials conventionally used for the cylindrical bodies of telescope tubes and is of sufficient stiffness to precisely hold the optics in their proper position. Wood is also excellent at absorbing minor vibrations that can be magnified into a degraded image. Normally, a telescope will cool in response to a drop in ambient temperature, such as occurs at night. Until the temperature of the telescope tube reaches equilibrium with the ambient temperature, convection currents transferring the dissipated heat from the telescope tube can invade the optical path, thereby degrading image sharpness and stability. Condensation can also cause problems in telescope tubes. Metal telescope tubes can take hours to reach equilibrium with the ambient temperature and are oftentimes coated with plastic, fiberglass or cork to impart more desirable thermal properties. Wood has a low specific heat and thusly stores minimal heat energy so that it is capable of cooling quickly to nighttime or other cooler air temperatures, such that air currents caused by heat transfer are avoided. Cardboard telescope tubes are oftentimes coated with plastic or fiberglass for increased strength and moisture resistance. The application of coatings to telescope tubes adds undesirable weight, manufacturing complexity and cost to the telescope tubes.
Wooden tube construction has been proposed comprising wooden strips attached to central support rings. Narrow width strips can be assembled to approximate a cylinder, but this requires a high level of craftsmanship and many parts. Cove and bead strips have been proposed for forming wooden tubes, but require fine finishing of both sides of each strip culminating in a very expensive finished product. Four, six or eight-sided wooden tubes are simpler and easier to make; however, the resulting tubes are not sufficiently cylindrical for smooth rotation about their longitudinal axes. Where the wooden strips are built on central support rings, the support rings are sometimes removed and discarded after the strips are laid. Accordingly, a new support ring is required for each tube to be constructed, which adds manufacturing complexity and cost. Sometimes the support rings are left in place, causing air currents along the tube to be thrown into the optical path resulting in degraded performance.
Telescopes that have altitude-azimuth telescope mounts permit a combination of vertical (altitude) and horizontal (azimuth) movements of the telescope tube to position the imaging end to find and/or track objects in the sky, which generally do not follow direct up and down (altitude) or side to side (azimuth) paths. To find and/or track objects in the sky with the imaging end of the telescope tube, altitude-azimuth telescope mounts combine vertical and horizontal movements to produce a fluidic composite movement. Many prior altitude-azimuth telescope mounts have not been successful at combining the vertical and horizontal movements to produce a composite movement that is smooth and accurate. Achieving a smooth composite motion made up of vertical and horizontal components has been so difficult to accomplish with altitude-azimuth telescope mounts that most serious astronomical viewing has been conducted using more expensive and complex equatorial telescope mounts. In addition, many prior altitude-azimuth telescope mounts do not permit fore and aft (longitudinal) adjustments and/or rotational adjustments of the telescope tube.
An altitude-azimuth telescope mount that successfully achieves fluidic altitude-azimuth motion of the telescope tube is the Dobson Telescope Mount. The Dobson Telescope Mount employs low friction bearing surfaces to address the problem of jerkiness associated with prior altitude-azimuth telescope mounts. In telescopes incorporating the Dobson Telescope Mount, a light aiming force or push on the telescope tube allows the telescope tube to be easily moved in a smooth, fluidic motion to obtain selected altitude-azimuth positioning. Upon removal of the aiming or pushing force, the telescope tube remains in and maintains the selected position. In addition, the Dobson Telescope Mount permits longitudinal and rotational adjustments of the telescope tube. In particular, the telescope tube may be balanced fore and aft, without using additional weights or springs, as eyepieces and tube-mounted accessories are changed and the telescope tube may be rotated about its central longitudinal axis for selectively positioning the eyepiece.
One significant drawback to the Dobson Telescope Mount is that the range of vertical (altitude) movement of the telescope tube is undesirably limited due to the telescope tube being obstructed by a rocker box of the Dobson Telescope Mount. In particular, a front board of the rocker box constrains vertical movement of the telescope tube to about a 90° vertical angle when pointing the imaging end at an object directly overhead. In order to follow the object beyond the range of vertical movement permitted by the Dobson Telescope Mount, the entire rocker box must be turned 180° and the direction of vertical movement for the telescope tube must be reversed in a maneuver that has become known as “the Dob Dance”. Removing the front board from the rocker box to allow the telescope tube to swing past vertical has been attempted, but has proven to be untenable since the front board provides essential structural support for other components of the Dobson Telescope Mount. In particular, the front board holds the side boards of the rocker box parallel, and eliminating the front board removes almost all lateral support for the side boards. Since the side boards support the altitude bearings, the altitude bearings are susceptible to misalignment where structural support for the side boards is removed. Another disadvantage of the Dobson Telescope Mount is that tracking of the bearings to prevent azimuth wobble is not adjustable and must rely on close tolerances to function effectively. A further drawback to the Dobson Telescope Mount is that the rocker box is heavy and adds considerable weight. The Dobson Telescope usually employs a cardboard telescope tube which disadvantageously lacks durability, strength and moisture-resistance.
It is desirable for telescope tubes to be adjustable longitudinally and rotationally. The capability for longitudinal movement or adjustment of a telescope tube fore and aft along its central longitudinal axis allows balance to be achieved as different eyepieces or accessories with different weights are attached to the telescope tube. Longitudinal adjustment allows the telescope tube to be balanced without using cumbersome springs or counterweights. Rotational movement or adjustment of a telescope tube about its central longitudinal axis allows the eyepiece to be placed conveniently for the user. For economy, many manufacturers of altitude-azimuth telescope mounts mount the altitude bearings directly to the telescope tube without a clamp assembly. Where the telescope tube is mounted directly to the altitude bearings, longitudinal adjustments cannot be made and balancing either is not possible or must be done with springs and/or counterweights. Rotational adjustments are also not possible, and the lack of longitudinal and rotational adjustments presents an impediment to optimal viewing and operation.
Tube clamps generally comprise at least two clamp members for engaging the tube at two different places along its length. Increasing the distance between the clamp members generally increases the rigidity of the clamp by increasing the length of the fulcrum from the clamping points to the balance point of the tube. Most tube clamp assemblies thusly comprise two or more essentially separate, individual clamp members which are operated separately each time the clamp members are locked (closed) or unlocked (opened) with respect to the tube. Accordingly, two or more separate operating actions are required to operate the clamp assemblies, and these multiple actions are oftentimes made more difficult by the fact that the operating members for the clamp members are usually located in an awkward place at the side of the tube. Operation of conventional tube clamp assemblies is, therefore, tedious and difficult. It is particularly difficult to operate conventional tube clamp assemblies by feel, especially in the dark.
Illustrative telescope mounts are represented by U.S. Pat. No. 3,751,134 and U.S. Pat. No. 3,893,746 to McMahon, U.S. Pat. No. 3,951,511 to Parsons, U.S. Pat. No. 4,470,672 to Drauglis, U.S. Pat. No. 4,764,881 to Gagnon, U.S. Pat. No. 5,124,844 to Wraight, and U.S. Pat. No. 5,416,632 to Carlisle. The McMahon patents disclose declination bearings rotatably mounted on planar walls of a support, and a cradle mounted to the declination bearings. A telescope tube passes through the cradle, and the cradle is adjustable to assume a desired declination angle. The Gagnon patent discloses bearings rotatably supported by vertical arms carried by a rotatable horizontal platform. The Parsons patent discloses a telescope tube held by two bands at spaced locations along the length of the telescope tube. The Drauglis patent discloses friction adjusters.
In light of the above, a need exists for an altitude-azimuth telescope mount allowing altitude and azimuth movements of a telescope tube to be combined in a fluidic composite motion while ensuring proper tracking of the altitude bearings of the telescope mount to prevent slippage and wobble. There is also a need for an altitude-azimuth telescope mount in which the effort required to rotate altitude bearings of the telescope mount is adjustable. Another need exists for an altitude-azimuth telescope mount which facilitates balancing of the effort required to move the telescope tube simultaneously and smoothly in both altitude and azimuth directions. A further need exists for an altitude-azimuth telescope mount incorporating a clamp assembly for a telescope tube wherein the clamp assembly comprises a plurality of clamp members opened and closed by operating a single operating member. An additional need exists for an altitude-azimuth telescope mount incorporating a plurality of clamp members having apertures through which a telescope tube passes, wherein the clamp members are movable to selectively vary the configuration of the apertures to selectively prevent and permit longitudinal and rotational movements of the telescope tube. A further need exists for a telescope tube having a body economically and aesthetically constructed of wooden slats assembled to form a sufficiently cylindrical configuration for unimpeded rotation of the telescope tube about its central longitudinal axis.